Carboxymethylcellulose, derived from the naturally-derived biomass cellulose, is a water-soluble derivative with good dispersibility and water retention, and it is therefore used in a variety of fields including foods and cosmetics. The high safety of carboxymethylcellulose allows it to be utilized in medical fields as a raw material for pap materials, X-ray contrast agents, tablet disintegrating materials, medicinal syrups and adhesion barriers.
Insoluble derivatives formed by modification of the carboxyl groups of carboxymethylcellulose are known, and an example thereof is disclosed in International Patent Publication No. WO01/046265, which describes a polyanionic polysaccharide water-insoluble derivative obtained by combining a carboxymethylcellulose-containing polyanionic polysaccharide, a nucleophilic reagent and an activating reagent in an aqueous mixture, as well as a method for producing it.
The derivative described therein is water-insoluble, and therefore the publication does not describe a gel according to the invention, which is a gel exhibiting a water-soluble property when present in a low concentration in water, but at high concentration exhibiting viscoelasticity such that it does not flow even when inclined.
International Patent Publication No. WO89/10940 describes total and partial esters of acidic polysaccharides selected from the group consisting of carboxymethylcellulose, carboxymethyl starch and carboxymethylchitin, with aliphatic, aryl aliphatic, alicyclic and heterocyclic alcohols, and salts of those partial esters with inorganic or organic bases. However, it makes no reference to formation of hydrogels by these polysaccharide derivatives, nor does it suggest providing an injectable gel according to the invention.
Japanese Patent Application Publication No. 2000-51343 discloses a natural wound-healing product comprising a polysaccharide polymer and one fatty acid chain attached to the polysaccharide polymer, which undergoes a reversible change of state from a gel to a liquid state and back.
However, the polysaccharides disclosed in these publications have poor viscoelasticity in aqueous solution, and therefore cannot be easily applied as hydrogels that are injectable into the body through narrow tubes such as injection needles.